Cardiac sarcoplasmic reticulum (SR) plays a dominant role in cellular Ca2+ homeostasis by storing and releasing Ca2+. SDS-polyacrylamide gel electrophoresis and Stains All staining reveals that at least six Ca2+- binding proteins are contained in cardiac SR vesicles, five of which have now been identified. These five SR proteins comprise a set of high capacity Ca2+-binding proteins, localized to the SR lumen, that exhibit properties expected for physiological Ca2+ stores. In this study, we have purified and isolated cDNA clones for the sixth major Stains All blue-staining protein of dog cardiac SR and identified it as GRP94 (glucose-regulated protein, M(r) = 94,000). Previously, this prominent Ca2+-binding component has only been described in non-muscle endoplasmic reticulum. Cardiac GRP94 co-sedimented with cardiac SR vesicles and all previously described SR markers and was completely contained within the SR lumen. GRP94, like several other SR Ca2+-binding proteins, was a substrate for casein kinase II and was phosphorylated at two or more sites located near the two ends of the molecule. A low level of endogenous casein kinase II activity was found in crude preparations of cardiac SR but did not co-purify with SR vesicles after calcium oxalate loading, suggesting that casein kinase II phosphorylation in vivo occurs at a site other than the SR.
|Original language||English (US)|
|Number of pages||6|
|Journal||Journal of Biological Chemistry|
|State||Published - Feb 25 1994|
ASJC Scopus subject areas
- Molecular Biology
- Cell Biology